Though a polysiloxane resin is excellent in thermal resistance, water repellency, weather resistance and the like, it has never been used alone because of its poor mechanical strength. Therefore, attempts have been made to use this resin for the modification of other kinds of resins such as acrylic resin, polyester resin or the like, thereby making the most of the excellent properties of said resin. However, in the heretofore proposed modification means, use is made of the reaction between silanol or alkoxy group contained in the polysiloxane resin and hydroxyl group contained in the organic base resin such as acrylic or polyester resin. Therefore, both resins are always connected with each other through Si--O--C bonding. Nevertheless, this Si--O--C bonding is liable to be easily hydrolyzed and hence the siloxane resin is regenerated by hydrolysis and gradually removed off, resulting in the decrease in corrosion resistance, weather resistance, stain resistance and the like of the coating.
In Japanese Patent Publication (unexamined) Sho 58-217515, Japanese Patent Publication Sho 58-58123 and the like, there has been proposed a modification of urethane resin with dimethylpolysiloxane having at both ends alcoholic hydroxyl groups. However, this leaves much to be desired because the crosslinking density is comparatively low and hence the surface hardness and mechanical strength of the formed coating are fairly of a lower order.
In Japanese Patent Publication Sho 60-1886 and 63-23212, there is an another proposal such that plural alcoholic hydroxyl groups are located at the side chain portions of polysiloxane resin, thereby increasing the crosslinking density. However, such resin can not be added in a quantity to the organic base resin because of its poor compatibility and hence it is hardly possible to obtain a thoroughly modified uniform resin.
It is, therefore, an object of the invention to provide measures for incorporating strongly a quantity of silicone resin into a base resin and provide a resinous composition for coating use by making use of said measures. It is an additional object of the invention to provide a resinous composition which is useful in a coating composition capable of resulting in a coating with excellent durability and weather resistance.